This invention relates generally to organ support and bypass processes, and more particularly to methods and apparatus for carrying out perfusion in a controlled manner.
Numerous medical procedures require extraction of a patient's blood, treatment of the blood by processes such as filtering, oxygenation, and the like, and return of the blood to the patient's body. Examples of such procedures include open heart surgery, organ transplants, membrane oxygenation, and hemodialysis. This type of blood processing is referred to herein as a “bypass” or “body support” process, and typically uses pumps with essentially constant pressure output to circulate the patient's blood through the treatment equipment. Unfortunately, this kind of flow is much different from the flow provided by a patient's heart. It has been found that this constant-pressure flow can have undesirable side effects including brain disorders, blood clot formation, and limited or reduced circulation, especially in flow restrictive areas. This places undesirable limits on the usage of this type of equipment.
It is also known that some devices use a similar process to circulate an aqueous organ preservation fluid, such as “Belzer's solution”, through organs which have been harvested for transplantation. This action sustains the organ while it is outside the body by attempting to preserve functioning, and increases the limited “shelf life” of transplant organs compared to conventional chilled storage. However, known organ support processes encounter the same problems as conventional bypass, namely that the flow pressure characteristics of the process fluid are much different than that provided by a patient's heart. Furthermore, flow which is only “pushed” by a pump is subject to the formation of gaseous, fibrinothrombocytic, and fat emboli which are difficult to remove, and which can interfere with flow and cause organ damage.